Synthesis, characterization, diastereoselectivity, and catalytic activity of complexes of ruthenium with BINAP monoxide

Article abstract of DOI:10.1021/om000014d

The bisphosphine monoxides (R)- and (S)-BINPO, prepared by the monoxidation of (R)-and (S)-BINAP, respectively, form complexes [CyRuCl(η²-BINPO-P,O)]X (X = Cl^-, (R)-BINPO, 1, (S)-BINPO, 1′; or SbF₆, 2 and 2′) and [CyRu(η²-BINPO-P,O)](SbF₆)₂, 3 and 3′. The new compounds were characterized spectroscopically and in the case of 2′ by single-crystal X-ray diffraction. The BINPO ligand binds diastereoselectively, and one observes only a single thermodynamically stable diastereomer of the two possible isomers. Compound 3 is an efficient catalyst for the condensation of methacrolein and cyclopentadiene in moderate ee.

Full text of DOI:10.1021/om000014d

Organometallics 2000, 19, 1829-1832
1829
Articles
Syn th esis, Ch a r a cter iza tion , Dia ster eoselectivity, a n d
Ca ta lytic Activity of Com p lexes of Ru th en iu m w ith
BINAP Mon oxid e
J . W. Faller*,† and J onathan Parr‡
Department of Chemistry, Yale University, 225 Prospect Street,
New Haven, Connecticut 06520, and Department of Chemistry, Loughborough University,
Loughborough, Leics LE11 3TU, U.K.
Received J anuary 7, 2000
The bisphosphine monoxides (R)- and (S)-BINPO, prepared by the monoxidation of (R)-
and (S)-BINAP, respectively, form complexes [CyRuCl(η2-BINPO-P,O)]X (X ) Cl-, (R)-
BINPO, 1, (S)-BINPO, 1′; or SbF6-, 2 and 2′) and [CyRu(η2-BINPO-P,O)](SbF6)2, 3 and 3′.
The new compounds were characterized spectroscopically and in the case of 2′ by single-
crystal X-ray diffraction. The BINPO ligand binds diastereoselectively, and one observes
only a single thermodynamically stable diastereomer of the two possible isomers. Com-
pound 3 is an efficient catalyst for the condensation of methacrolein and cyclopentadiene in
moderate ee.
In tr od u ction
mediates.3,4 Third, coordination of a BPMO to a frag-
ment of the type [(arene)MX] (arene ) η6-C6H6 or
derivative, η5-(C5H5)- or derivative, M ) transition
metal, X ) Cl-, etc.) yields a chiral metal center,5 which
may further enhance the selectivity of such a reagent.
As part of our continuing study of the application of
heterobidentate ligands to homogeneous catalysis,6
we report here the preparation, characterization, and
catalytic behavior of complexes of ruthenium(II) with
BINPO (monoxidized BINAP).
There has been an increasing interest in chelating
ligands that contain mixed donor sets. Complexes of
such ligands offer a number of attractive features,
especially in the case of complexes that have potential
application in homogeneous catalysis. One feature is
that the different donors can produce an electronic
asymmetry at the metal. Another is that the ligands
may be hemilabile. With this in mind, a number of
groups have developed the use of bisphosphine monox-
ide (BPMO) ligands in coordination chemistry.1
Resu lts a n d Discu ssion
A report has appeared recently giving an efficient
route to BPMO ligands derived from well-known bis-
phosphine ligands, including a number of commercially
available chiral examples.2 The monoxidized forms of
these ligands offer some features not available to their
unoxidized counterparts. First, upon chelation, they give
rise to complexes that have a more pronounced steric
asymmetry, as the organic substituents attached to the
P(III) are very much closer to the metal center than
those on the P(V). Second, the two donor atoms are now
markedly dissimilar, and their different electronic
properties may have a significant influence upon the
bonding of other ligands coordinated to the metal center,
thereby altering the stereochemistry of reaction inter-
The interaction of [CyRuCl2]2 with either (R)- or (S)-
BINPO in dichloromethane gives a deep red solution
with a complex 31P{1H} NMR spectrum. Upon standing
at room temperature for 48 h, the spectrum simplifies
greatly to an AX pattern typical of η2 coordination of a
BPMO ligand. The chelation gives the complex [CyRuCl-
(η2-BINPO-P,O)]Cl (for (R)-BINPO, 1; (S)-BINPO, 1′),
which is chiral at the metal center. Since only one set
of resonances is observed in the NMR spectra of both 1
and 1′, it seems that one of the two possible η2-isomers
is thermodynamically preferred in each case (see Figure
1). This suggests that chelation proceeds diastereose-
lectively, Scheme 1. Anion metathesis of these com-
pounds gives the hexafluoroantimonate salts 2 and 2′;
the latter was characterized crystallographically and is
† Yale University.
‡ Loughborough University.
(1) (a) Faller, J . W.; Patel, B. P.; Albrizzio, M. A.; Curtis, M.
Organometallics 1999, 18, 3096. (b) Coyle, R. J .; Slovotkhotov, Yu. L.;
Antipin, M. Yu.; Grushin, V. V. Polyhedron 1998, 17, 3059. (c) Brassat,
I.; Englert, U.; Keim, W.; Keitel, D. P.; Killat, S.; Suranna, G.-P.; Wang,
R. Inorg. Chim. Acta 1998, 280, 150. (d) Vicente, J .; Arcas, A.; Bautista,
D.; J ones, P. G. Organometallics 1997, 16, 2127. (e) Bader, A.; Lindner,
E. Coord. Chem. Rev. 1991, 108, 27.
(3) (a) Faller, J . W.; Mazzieri, M. R.; Nguyen, J . T.; Parr, J .;
Tokunaga, M. Pure Appl. Chem. 1994, 66, 1463-1469. (b) Nomura,
N.; MermetBouvier, Y. C.; RajanBabu, T. V. Synlett 1996, 745. (c)
RajanBabu, T. V.; Casalnuovo, A. L. J . Am. Chem. Soc. 1996, 118, 6325.
(4) Schnyder, A.; Togni, A.; Wiesli, U. Organometallics 1997, 16, 255.
(5) Brunner, H. Adv. Organomet. Chem. 1980, 18, 151; Ann. N. Y.
Acad. Sci. 1974, 239, 213;
(2) Grushin, V. V. J . Am. Chem. Soc. 1999, 121, 5831.
10.1021/om000014d CCC: $19.00 © 2000 American Chemical Society
Publication on Web 03/31/2000

1830 Organometallics, Vol. 19, No. 10, 2000
Faller and Parr
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [CyRu Cl(η2-(S)-BINP O-P ,O)]SbF 6, 2′
Ru(1)-Cl(1)
Ru(1)-O(1)
2.388(2)
2.138(4)
Ru(1)-P(1)
P(2)-O(1)
2.395(2)
1.493(4)
Cl(1)-Ru(1)-P(1)
P(1)-Ru(1)-O(1)
84.68(7)
81.5(1)
Cl(1)-Ru(1)-O(1)
Ru(1)-O(1)-P(2)
87.6(2)
165.9(3)
Ta ble 3. Ca ta lysis of th e Diels-Ald er Rea ction of
Meth a cr olein a n d Cyclop en ta d ien e by 3
reaction temperature
ee
mol % time (h)
(°C)
base
(%)
exo:endo
10
10
10
10
5
12
12
18
18
18
18
-12.0
-12.0
-24.0
-24.0
-24.0
-24.0
5 (R)
lutidine 19 (R)
27 (R)
lutidine 50 (R)
24 (R)
lutidine 47 (R)
5.6:1
10.4:1
5.4:1
9.9:1
5.5:1
9.8:1
F igu r e 1. ORTEP view of the cation in (RRu)-[CyRuCl(η2-
(S)-BINPO-P,O)]SbF6, 2′, with 50% probability ellipsoids.
Sch em e 1a
5
the relative configuration of R*S*. Although there might
be expected to be some modest flexibility from rotation
about the bond connecting the naphthyl groups, they
are approximately at right angles with a dihedral angle
between them of 83.6°.
The configuration of the binaphthyl portion of the
ligand apparently forces a configuration of the Ph2P
fragment that sterically controls the preference for
direction of chelation. The ligand backbone requires an
unusually large Ru-O-P angle of 165.9(3)°. Even
though there is an eight-membered chelate ring, it
produces a quite small bite angle of 81.5(1)°.
a
(i) 48 h, CH2Cl2, 25 °C. (ii) AgSbF6, (-AgCl) CH2Cl2, 25
°C. (iii) 2 AgSbF6 (-2 AgCl) CH2Cl2, 25 °C.
Although the coordination about the metal can be
considered pseudotetrahedral, one should note that all
of the angles between the P, O, and Cl are less than
90°. Comparison with the dppmO analogue, which has
a five-membered chelate ring, produces only a slightly
smaller bite angle of 80.8°.1a The chiraphosO analogue,
with six-membered chelate rings, has larger bite angles
of 82.2(4)° or 83.8(3)° depending upon the diastereomer.6
Further treatment of 2 or 2′ with AgSbF6 or sequen-
tial reaction of 2 equiv of BINPO and 4 equiv of AgSbF6
with [CyRuCl2]2 gives the doubly charged complex ions
[CyRu(η2-BINPO-P,O)](SbF6)2, 3 and 3′. The likelihood
of the cation in 3 or 3′ existing as coordinatively
unsaturated species as written is limited, especially in
solution, where they probably exist as solvates, but since
the exact nature of the compounds is uncertain, they
are written here as the “free” Lewis acids.
This dipositive cation is a strong Lewis acid, and 3
can be used to catalyze the condensation of cyclopen-
tadiene and methacrolein.6 We had observed very mod-
est enantioselectivity in this reaction with the chira-
phosO analogue; however, [CyRuX(η2-chiraphosO-P,O)]2+
complexes are not formed with as high diastereoselec-
tivity at the metal center7 as found for the BINPO
complex. The six-membered chelate ring for the chira-
phos derivative assumes a boat conformation in one
diastereomer and a chair conformation and thus accom-
F igu r e 2. The two possible diastereomers of a [CyRuCl-
(η2-BINPO-P,O)]+ cation.
Ta ble 1. Cr ysta llogr a p h ic Da ta for X-r a y
Diffr a ction Stu d y of
(RRu )-[CyRu Cl(η2-(S)-BINP O-P ,O)]SbF 6, 2′
formula
cryst syst
space group
a, Å
b, Å
c, Å
SbRuClP2F6OC54H46
monoclinic
P21 (No. 4)
12.3028(2)
15.2403(4)
12.9278(2)
97.600(1)
2402.65(7)
1145.17
1.583 (Z ) 2)
10.60
0.17× 0.07 × 0.02
Nonius KappaCCD
graphite
Mo KR (0.71073 Å)
55
32 346
3584
594
0.01
â, deg
V, Å3
fw
F
calcd, g/cm3
abs coeff (cm-1
cryst size, mm
diffractometer
)
monochromator
radiatn
max 2θ, deg
no. of refl measured
no. of data used, F2 > 3σ(F2)
no. of params refined
p factor
final residuals R, Rw
convergence, largest shift/error
GOF
0.033, 0.036
0.00
0.93
largest ∆(F), e Å-3
1.14
modates the steric interactions associated with the (RRu
)
and (SRu) more readily than BINPO, which does not
have the same options. This suggested that the BINPO
derivative should yield better enantioselectivity. Some
results for this reaction with 3 are presented in Table
3. Compound 3 is the first example of a BINPO-
supported Lewis acid used to catalyze a Diels-Alder
shown in Figure 2. Crystal data and solution param-
eters are given in Table 1 and metrical parameters in
Table 2. The same compound can be prepared directly
from the sequential addition of 2 equiv of BINPO and 2
equiv of AgSbF6 to a solution of [CyRuCl2]2.
The (RRu)-[CyRuCl(η2-(S)-BINPO-P,O)]SbF6 structure
found for 2′ shows that the preferred diastereomer has
(6) Faller, J . W.; Liu, X.; Parr, J . Chirality 2000, in press.

Complexes of Ru with BINAP Monoxide
Organometallics, Vol. 19, No. 10, 2000 1831
ture method.2 The NMR spectra were recorded of solutions in
CDCl3 at 500.08 MHz (1H) or 202.43 MHz (31P) on a GE Omega
500 spectrometer. Chemical shifts are reported in ppm rela-
tive to residual protio solvent resonances (1H) or external 85%
H3PO4 (31P). Microanalyses were performed by Atlantic Mi-
crolabs. For brevity, details of the preparation and character-
ization of 1-3 only are given.
reaction. The enantiomeric excess observed in the
product is enhanced by the addition to the catalytic
reaction of half an equivalent of 2,6-lutidine (with
respect to the ruthenium), as is the exo:endo ratio. The
influence of a noncoordinating base on the course of the
reaction is most likely the suppression of any catalysis
by other competing Lewis acids in solution, such as
unligated metal ions or protons arising from adventi-
tious water in the reaction mixture.8 Since the incor-
poration of base into the catalytic reaction system
results in an increase in selectivity, for both ee and exo:
endo, it can be inferred that the nonenantioselective
production of the bicyclic aldehyde is promoted by such
stray acid. The origin of the decreased formation of the
endo isomer is less obvious. The R-substituent on the
methacrolein favors exo isomer formation, even for the
thermal reaction (exo:endo ≈ 5:1), and acid catalysis
usually results in larger exo:endo ratios. Kundig et al.7a
have suggested that hydrogen bonding to anions has a
significant effect on rate and to some minor extent on
ee. The addition of base could possibly compete for
hydrogen-bonding sites and alter the ion pairing. In the
crystal structure of 2 there are several close contacts
between fluoride and H on the ligands, which might be
considered weak hydrogen bonds;9 for example there is
a 2.25 Å distance between a cymene C-H (at 1.09 Å)
and an F on the SbF6-. There certainly would be ion
pairing in solution, regardless of the nature of the inter-
actions, and it could be altered by additives. Alterna-
tively, donor-acceptor interactions of the lutidine with
the reactants could be the source of the variation in exo:
endo ratio, unrelated to a proton-catalyzed path.
P r ep a r a t ion of [CyR u Cl(η2-BINP O-P ,O)]Cl, 1. (R)-
BINPO (27 mg, 0.042 mmol) was added as a solid to a
dichloromethane solution (5 mL) of [CyRuCl2]2 (13 mg, 0.021
mmol). The solution darkened to a deep red over a period of 2
h. After 48 h, the solvent was removed and the residue
recrystallized in quantitative yield from dichloromethane-
diethyl ether. 1H NMR (CDCl3, 293 K, δ): 8.15-6.48 (32 H,
m, aromatic) 6.10 (1H, d, J ) 6 Hz, CyC-H) 5.98 (1H, d, J )
6 Hz, CyC-H) 5.72 (1H, d, J ) 6 Hz, CyC-H) 5.40 (1H, d, J
) 6 Hz, CyC-H) 2.46 (1H, septet, J ) 7 Hz CyCH(CH3)2) 1.29
(3H, s, CyCH3) 1.18 (3H, d, J ) 7 Hz, CyCH(CH3)-CH3) 0.98
(3H, d J ) 7 Hz, CyCH(CH3)-CH3). 31P{1H} NMR: P(V) 40.01
3
3
(d, J 31P 63 Hz) P(III) 24.77 (d, J 31P 63 Hz). Anal. Calcd for
54H46OP2Cl2Ru: C, 68.64; H, 4.91. Found: C, 68.40; H, 5.07.
ν(PdO) (KBr): 1094 cm-1
C
.
P r ep a r a t ion of [CyR u Cl(η2-BINP O-P ,O)]Sb F 6, 2. (R)-
BINPO (27 mg, 0.042 mmol) was added as a solid to a
dichloromethane solution (5 mL) of [CyRuCl2]2 (13 mg, 0.021
mmol). The solution darkened to a deep red over a period of 2
h. AgSbF6 was added (14 mg, 0.042 mmol) as a solution in
dichloromethane (1 mL). A white precipitate of AgCl formed
immediately, and after 10 min of stirring, the reaction mixture
was centrifuged and the supernatant removed by syringe. The
solvent was removed from the supernatant fraction and the
residue recrystallized in quantitative yield from dichlo-
1
romethane-diethyl ether. H NMR (CDCl3, 293 K, δ): 8.15-
6.50 (32 H, m, aromatic) 6.12 (1H, d, J ) 6 Hz, CyC-H) 5.99
(1H, d, J ) 6 Hz, CyC-H) 5.68 (1H, d, J ) 6 Hz, CyC-H) 5.44
(1H, d, J ) 6 Hz, CyC-H) 2.48 (1H, septet, J ) 6.5 Hz
CyCH(CH3)2) 1.25 (3H, s, CyCH3) 1.14 (3H, d, J ) 6.5 Hz,
CyCH(CH3)-CH3) 0.98 (3H, d, J ) 6.5 Hz, CyCH(CH3)-CH3).
Con clu sion s
3
31P{1H} NMR: P(V) 40.10 (d, J P-P ) 61 Hz) P(III) 26.14 (d,
The unusually large metal-P-O bond angle in the
BINPO complex provides a particularly low steric
requirement at the PdO donor site, compared to that
of the Ph2P donor site. We anticipate that this steric
differential, in addition to the electronic asymmetry
provided by the P,O-donor set, may be ultimately useful
in a broader set of catalytic Lewis acid reactions, and
we are currently investigating the use of this and other
metal-BINPO complexes as Lewis acid catalysts.
3J P-P ) 61 Hz). Anal. Calcd for C54H46OF6P2ClRuSb: C, 56.64;
H, 4.05. Found: C, 56.14; H, 4.34. ν(PdO) (KBr): 1096 cm-1
.
P r ep a r a tion of Solu tion s of [CyRu (η2-BINP O-P ,O)]-
(SbF 6)2, 3. Compound 3 was prepared in situ for catalytic
reactions and was characterized spectroscopically. BINPO (27
mg, 0.042 mmol) was added as a solid to a dichloromethane
solution (5 mL) of [CyRuCl2]2 (13 mg, 0.021 mmol). The
solution darkened to a deep red over a period of 2 h. AgSbF6
was added (29 mg, 0.084 mmol) as a solution in dichlo-
romethane (1 mL). A white precipitate of AgCl formed im-
mediately, and after 10 min of stirring, the reaction mixture
was centrifuged and the supernatant removed by syringe. The
solution was used directly for the catalytic reactions. 1H NMR
(CDCl3, 293 K, δ): 8.12-6.4 (32H, m, aromatic) 6.28 (1H, d, J
) 5.9 Hz, CyC-H) 6.10 (1H, d, J ) 5.9 Hz, CyC-H) 5.88 (1H,
d J ) 5.9 Hz, CyC-H) 5.61 (1H, d J ) 5.9 Hz, CyC-H) 2.61
(1H, septet, J ) 7 Hz CyCH(CH3)2) 1.41 (3H, s, CyCH3) 1.22
(3H, d, J ) 7 Hz, CyCH(CH3)-CH3) 1.08 (3H, d, J ) 7 Hz,
CyCH(CH3)-CH3). 31P{1H} NMR: P(V) 66.37 (s) P(III) 52.18
Exp er im en ta l Section
All manipulations were performed under an atmosphere of
nitrogen using standard Schlenk and drybox techniques.
Solvents were dried and distilled before use according to
published protocols.10 AgSbF6 and BINAP were obtained from
a commercial source (Aldrich) and used as received. [CyRuCl2]2
was prepared according to literature methods.11 (R)-BINPO
and (S)-BINPO were prepared by a recently published litera-
(s). ν(PdO) 1022 cm-1
.
(7) (a) Kundig, E. P.; Saudan, C. M.; Bernardinelli, G. Angew. Chem.,
Int. Ed. 1999, 38, 1220 (Ru). (b) Davenport, A. J .; Davies, D. L.;
Fawcett, S. A.; Garratt, S. A.; Lad, L.; Russell, D. R. Chem. Commun.
1997, 2345 (Rh). (c) Davies, D. L.; Fawcett, S. A.; Garratt, S. A.; Russell,
D. R. Chem. Commun. 1997, 1351 (Ru). (d) Carmona, D.; Cativicla,
C.; Garcia-Correas, R.; Lahoz, F. J .; Lamata, M. P.; Lopez, J . A.; Lopez-
Ram de Viu, M. P.; Oro, L. A.; San J ose, E.; Viguri, F. Chem. Commun.
1996, 1242 (Rh). (e) Evans, D. A.; Murray, A.; von Matt, P.; Norcross,
R. D.; Miller, S. J . Angew. Chem., Int. Ed. Engl. 1995, 34, 798 (Cu). (f)
Hollis, T. K.; Robinson, N. P.; Bosnich, B. Organometallics 1992, 11,
2745 (Ti, Zr). (g) Kagan, H.; Riant, O. Chem. Rev. 1992, 92, 1007.
(8) Hanamoto, T.; Furono, H.; Sugimoto, Y.; Inanaga, J . Synlett.
1997, 79.
X-r a y Cr ysta llogr a p h y. Single crystals suitable for X-ray
analysis were formed by vapor diffusion of diethyl ether into
a methanol solution of 2′. Crystallographic data are sum-
marized in Table 1. The structure of 2′ was determined from
data collected with a Nonius KappaCCD at -90 °C. Lorentz
and polarization corrections were applied to all data. An
empirical absorption correction was applied using SORTAV.12
(10) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory
Chemicals, 3rd ed.; Pergammon Press: New York, 1988.
(11) Bennett, M. A.; Huang, T.-N.; Matheson, T. W.; Smith, A. K.
Inorg. Synth. 1981, 21, 74.
(9) Grepioni, F.; Cojazzi, G.; Draper, S. M.; Scully, N.; Braga, D.
Organometallics 1998, 17, 296-307.

1832 Organometallics, Vol. 19, No. 10, 2000
Faller and Parr
Intensities of equivalent reflections, excluding Friedel pairs,
were averaged. The structure was solved by direct methods
(SIR9213) using the teXan crystal structure analysis package,
and the function minimized was ∑w(|Fo| - |Fc|)2 in all cases.
Hydrogen atoms were placed at calculated positions before
each refinement and were included in the refinement, but were
not refined. Large thermal parameters for the cymene isopro-
pyl group were observed, indicating a small disorder in the
orientation of the isopropyl group. The absolute configuration
was determined by reference to the configuration of the (S)-
BINPO. This was confirmed by refinement of the inverted
structure, which gave R ) 0.035 and Rw ) 0.040; whereas the
reported coordinates gave R ) 0.033 and Rw ) 0.036. This (+)-
(RRu)-[CyRuCl(η2-(S)-BINPO-P,O)]SbF6 shows a positive CD
band at 490 nm and a negative CD band at 392 nm.
Ack n ow led gm en t. The authors thank M. Albrizzio
for useful discussions. This research was supported by
a grant from theNationalScienceFoundation (CHE9726423).
Su p p or tin g In for m a tion Ava ila ble: Tables of crystal
data, positional and thermal parameters, and bond lengths
and angles for 2′. This material is available free of charge via
the Internet at http://pubs.acs.org.
(12) Blessing, R. H. Acta Crystallogr. 1995, A51, 33-37. Blessing,
R. H. J . Appl. Crystallogr. 1997, 30, 421-426.
(13) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.;
Giacovazzo, C.; Guagliardi, A.; Polidori, G. J . Appl. Crystallogr. 1994,
27, 435.
OM000014D